Exposure apparatus and device manufacturing method including gas purging of a space containing optical components

ABSTRACT

An exposure apparatus includes an illumination optical system for illuminating an original with an F 2  excimer laser, a projection optical system for projecting a pattern of the original onto a substrate to be exposed, a gas purging device for replacing a gas in an inside space, which accommodates optical components of at least one of the illumination optical system and the projection optical system, with a dry gas, a hygrometer, disposed in the inside space, for measuring conditions in the inside space and for producing an output, and a controller for controlling the gas purging device on the basis of the output of the hygrometer.

This application is a divisional of copending application Ser. No.09/145,982, filed Sep. 3, 1998.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to an exposure apparatus and a devicemanufacturing method. More particularly, the invention is concerned withan exposure apparatus for use in an exposure process for the manufactureof various devices such as semiconductor devices (e.g., ICs or LSIs),image pickup devices (e.g., CCDs), display devices (e.g., liquid crystalpanels), or sensors (e.g., magnetic heads), for example, and it isconcerned with a device manufacturing method for manufacturing devicessuch as described above.

For further increases of integration and operation speed of a soliddevice such as an LSI, for example, miniaturization of a circuit patternis being advanced. Currently, pattern formation uses a lithographicprocess which is based on a reduction projection exposure method havingsuperiority in productivity and resolution performance. In this method,a circuit pattern of a mask is simultaneously transferred to a workpiecesuch as a semiconductor wafer by use of a projection lens. The limitresolution performance is proportional to the wavelength of exposurelight and is in an inverse proportion to the numerical aperture (NA) ofthe projection lens. In consideration of this, improvement of resolutionhas been attempted by enlargement of the numerical aperture of theprojection lens. However, further miniaturization of semiconductordevices needs shortening of the wavelength of the exposure light.

Recently, an addition to illumination light of a Hg lamp of e-line(wavelength λ=546 nm), g-line (λ=435 nm), h-line (λ=405 nm) or i-line(λ=365 nm), short wavelength excimer lasers (e.g., a KrF excimer laserwith λ−248 nm) are used practically in an exposure apparatus.

Even if a high resolution projection lens and a short wavelength andhigh luminance light source are used, uniform resolution is notattainable over the whole circuit pattern image as printed on a waferunless the illuminance distribution (light intensity distribution) oflight illuminating the photomask is not uniform. Thus, good patternprinting is not accomplished. For this reason, an illumination opticalsystem of a projection exposure apparatus must provide illuminanceuniformness of illumination light to be projected to a mask surface, toassure uniform exposure over the whole printing surface. To this end,conventionally an illumination optical system is disposed between alight source and a mask surface, which optical system comprises acondenser lens and an optical integrator including an optical fiberbundle or a lens array called a fly's eye lens. In excimer laserexposure apparatuses, as a result of the use of a larger numericalaperture of a projection lens and a shorter wavelength of the lightsource for higher resolution precision and productivity, it is much moreimportant to maintain illuminance uniformness (not greater than ±1%)than in other exposure apparatuses.

However, practically it is very difficult to maintain illuminanceuniformness of not greater than ±1% for a long time period.

Short wavelength exposure light such as described above may be extractedout of a wide bandwidth range of a light source, comprising a Hg lamp,for example, by use of a filter for transmitting only a desiredwavelength or a wavelength selective thin film (optical thin filmdeposited on a lens surface or a mirror surface for transmitting orreflecting a desired wavelength only). Exposure light emitted from alight source goes through an illumination optical system forilluminating a reticle and a projection optical system (projection lens)for imaging a fine pattern, as formed on the reticle, upon aphotosensitive substrate, by which transfer and printing of the finepattern onto the photosensitive substrate is performed. In exposureapparatuses, because of miniaturization of the pattern line width,improvements of throughput and resolution are required, and thisnecessitates the use of higher power exposure light and, additionally, anarrowed bandwidth of exposure light.

It is known that, in an exposure apparatus using exposure light ofi-line (wavelength λ=365 nm) and an exposure apparatus using exposurelight of a wavelength shorter than the i-line, as a result of theshortening of the wavelength, the exposure light causes an opto-chemicalreaction between oxygen and impurities in the air. There is aninconvenience that the product (blurring materials) created by thisreaction adheres to a glass material to cause an opaque “blur” on theglass material. As for such a blurring material, there by ammoniumsulfate (NH₄)₂SO₄, as a representative, which can be produced when, forexample, sulfurous acid absorbs energy of the light and turns into anexcited state such that it reacts with oxygen in the air (i.e., isoxidized). Such ammonium sulfate bears a white color, and it produces a“blur” when deposited on the surface of an optical component such as alens or a mirror. In that case, the exposure light is scattered orabsorbed by the ammonium sulfate and, as a result, the transmissionfactor of the optical system decreases.

Particularly, in the short wavelength region as of a KrF excimer laser,for example, wherein the exposure light has a wavelength of about 248 nmwhich is shorter than the i-line, the exposure light may cause a strongopto-chemical reaction. In addition to production of “blur” as describedabove, there may be a phenomenon that the exposure light causes afurther reaction of oxygen in the air to produce ozone such that bothresidual oxygen and produced ozone absorb the exposure light. Thisresults in a further decrease of the light quantity (transmissionfactor) of exposure light which can reach the photosensitive substrate,and it causes a reduction of throughput. Japanese Laid-Open PatentApplication, Laid-Open No. 216000/1994 proposes the use of a casing of asealingly closed structure which accommodates therein a barrelcontaining a glass member such as a lens, for example, inside of thecasing being filled with an inert gas to keep a low oxygen density tothereby prevent ozone generation.

With this method, however, attenuation or variation of exposure lightresulting from absorption of exposure light by “blur” or ozone cannot beprevented sufficiently.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide anexposure apparatus and/or a device manufacturing method by which anychange in illuminance or illuminance non-uniformness can be suppressedsuch that a substrate can be exposed constantly with a correct exposureamount.

In accordance with an aspect of the present invention, there is providedan exposure apparatus, comprising: an illumination optical system forilluminating an original with ultraviolet light; a projection opticalsystem for projecting a pattern of the original onto a substrate to beexposed; and gas purging means for replacing an inside space, whereoptical components of at least one of said illumination optical systemand said projection optical system are placed, with a gas containingsubstantially no moisture or water content.

In accordance with another aspect of the present invention, there isprovided an exposure apparatus, comprising: an illumination opticalsystem for illuminating an original with ultraviolet light; a projectionoptical system for projecting a pattern of the original onto a substrateto be exposed; gas purging means for replacing an inside space, whereoptical components of at least one of said illumination optical systemand said projection optical system are placed, with a particular gas;and passage means for mutually communicating spaces separated by saidoptical components, for gas purging.

In an illumination optical system or a projection optical system of areduction projection exposure apparatus, an anti-reflection film(optical thin film) is formed on the surface of an optical element suchas a transparent plate, a lens or a prism, for example. The provision ofsuch an anti-reflection film is to efficiently direct light from a lightsource to a photosensitive substrate and also to prevent impingement ofa flare or ghost on the photosensitive substrate. However, due to theproperty, such anti-reflection film may easily absorb the water contentof gas. With an anti-reflection film having a water content adheredthereto, the spectral reflection characteristic on the surface thereofor the absorption coefficient on the surface may change by a smallamount, causing a change in the spectral transmission factor. Usually,an illumination optical system and a projection optical system haveoptical elements with surfaces of a number of several tens in total.Thus, even if the change in spectral transmission factor per one surfaceis small, there may be a large change of spectral transmission factor inthe whole optical system.

In accordance with the first aspect of the present invention, theambience of optical components of the illumination optical system or theprojection optical system may be replaced by a gas having substantiallyno water content, by gas purging. This is effective to prevent a changein transmission factor of the whole optical system (i.e., a change inilluminance or illuminance non-uniformness) resulting from a change inspectral transmission factor due to adhesion of water content to opticalelements such as described above. Thus, a substrate can be exposedconstantly with a correct exposure amount.

Absorption of exposure light or generation of “blur” material in a casewhere oxygen or ozone is present along the light path may be solved byaccommodating optical components such as lenses in a casting of asealingly closed structure and by filling the casing inside with aninert gas to thereby keep a low oxygen density. However, in a barrelwhere lenses are placed, there are spaces which are separated by lensesand the barrel structure. Proper gas replacement cannot always be donewithin these spaces. Namely, it is not easy to effectively preventabsorption of exposure light or generation of “blur” material.

In accordance with the second aspect of the present invention, theambience of optical components of the illumination optical system or theprojection optical system may be replaced by an inert gas, by gaspurging. Additionally, there may be passage means communicated with thecasing inside or the barrel inside, by which a low oxygen density can bekept within the space where glass materials are placed. This effectivelyprevents an oxidization reaction during an opto-chemical reactionprocess, and avoids generation of a resultant product (blurringmaterial). Additionally, it effectively prevents or reduces ozonegeneration due to reaction oxygen by exposure light.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a general structure of a projectionexposure apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic view of an inside structure of an illuminationoptical system or a projection optical system.

FIG. 3 is a schematic view for explaining passage of a purging airinside an illumination optical system or a projection optical system.

FIG. 4 is a graph for explaining changes in transmission factor withrespect to time, in a case where laser irradiation and gas purging arenot performed and the apparatus is left for a while.

FIG. 5 is a schematic view of a general structure of a projectionexposure apparatus according to a second embodiment of the presentinvention.

FIG. 6 is a schematic view of a general structure of an exposureapparatus according to a third embodiment of the present invention.

FIG. 7 is a schematic view for explaining an example of an insidestructure of a casing and barrel of the FIG. 6 embodiment.

FIG. 8 is a schematic view of lenses to be used in the FIG. 6embodiment, with notches outside the effective light flux.

FIG. 9 is a flow chart of microdevice manufacturing processes.

FIG. 10 is a flow chart for explaining details of a wafer processincluded in the procedure of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A reduction projection exposure apparatus according to an embodiment ofthe present invention may comprise means for replacing ambient air ofoptical components of an illumination optical system and/or a projectionoptical system with a gas such as N₂ gas, He gas or dry air, forexample. This is effective to decrease the humidity inside the opticalsystem, to reduce adhesion of moisture (water content). Thus, a changein a spectral reflection factor of anti-reflection films can beprevented, and the transmission factor of the optical system can bemaintained substantially constant.

A sensor such as a humidity sensor, for example, for detecting the levelof replacement by the gas purging may be provided inside the opticalsystem, and the gas purging may be controlled on the basis of a signalfrom the sensor.

For efficient gas purging, an inlet port and an outlet port for thepurging gas inside the optical system may be disposed along anon-straight line.

In each optical system, support members for supporting lenses areprovided with passages for gas purging, which passages are so formedthat in adjacent support members the passages are not aligned along astraight line. This assures higher replacement efficiency inside thebarrel.

A reduction projection exposure apparatus according to anotherembodiment of the present invention may provide an exposure apparatuswherein a mask is illuminated with exposure light form a light sourcethrough an illumination optical system and wherein a pattern formed onthe mask is projected onto a photosensitive substrate through aprojection optical system. The exposure apparatus may include an opticalelement or elements disposed on a light path of exposure light from theexposure light source to the photosensitive substrate, and a casing foraccommodating the optical element or elements therein. The opticalelement or each optical element is formed with a notch for positivelydefining a flow passage of gas between spaces inside the casing, beingseparated by the optical element.

In order to accomplish the second aspect of the invention, as anexample, within the barrel where a number of lenses may be placed, thelens supports may be provided with flow passages for flowing inert gasinto every space as separated by the lenses. Alternatively, pipe meansmay be used to define a flow passage outside the barrel.

On the other hand, as a result of further miniaturization and furtherenlargement of throughput, projection exposure apparatuses have becomebulky and complicated. Thus, for every unit, saving as much space aspossible is desired. In this respect, if a flow passage is formed in thelens support, the diameter of the barrel with respect to the effectivelight flux becomes larger. Further, using pipe means to provide a flowpassage outside the barrel leads to undesirable complexity and increaseof cost.

In the above embodiment, in consideration of this, an end portion of alens is cut to save the space. More specifically, a notch may be definedoutside the effective range of a lens or optical component which is usedwhen in a projection exposure apparatus a reticle is illuminated withexposure light from a light source so that a pattern of the reticle istransferred to a wafer through a projection lens. This may be done toassure a flow passage for inert gas. This enables provision of a flowpassage without the use of specific components of pipe means and withoutenlargement of the barrel diameter. In recent years, scan typeprojection exposure apparatuses are practically developed. For theseexposure apparatuses, since the effective light flux is small ascompared with the projection exposure apparatus, the design may beeasier.

Preferred embodiments of the present invention will now be described inconjunction with the drawings.

FIG. 1 is a schematic view of a general structure of a projectionexposure apparatus according to a first embodiment of the presentinvention. Denoted in the drawing at 1 is a light source which maycomprise an excimer laser of KrF (248 nm), ArF (193 nm) or F₂ (157 nm),for example. Denoted at 2 and 3 are illumination optical systems.Denoted at M1, M2 and M3 are deflecting mirrors. The illuminationoptical system 2 or 3 may include a beam shaping optical system forshaping and incoherency transforming the laser light from the lightsource 1, as well as a fly's eye lens for defining secondary lightsources and a condenser lens, for example. The light from theillumination optical system 3 is projected to a reticle R, such that thereticle is projected onto a photosensitive substrate (wafer) W by meansof a projection optical system 4. Denoted at 5 is an X-Y stage forholding the photosensitive substrate W, and it performs two-dimensionalstepwise motion in X and Y directions. Each of the illumination opticalsystems 2 and 3 and the projection optical system 4 is provided with agas supply tube and a gas discharging tube for replacing and purging thegas within the inside space thereof.

FIGS. 2 and 3 show the structure in the inside space of the illuminationoptical system 2 or 3 of the projection optical system 4. A casing 20for the optical system is provided with an inlet port 6 and an outletport 7 which are formed in a side wall of the casing and to which tubesfor gas purging are connected. Inside the casing 20, lenses 30 aresupported by lens support members 31, respectively. For efficient anduniform replacement of the whole inside space with purging air, eachlens support 31 is formed with bores to provide purging air passages 32which are so disposed that at adjacent lenses the passages 32 are notaligned along a straight line. Namely, a straight line connecting thepassages 32 of adjacent lens supports 31 is out of parallel to anoptical axis of the lens 30. With this arrangement, the path of air flowdefined from the inlet port 6 to the outlet port 7 is not straight.

FIG. 4 illustrates changes in transmission factor with respect to time,in a case where the apparatus is left without laser projection and gaspurging. With the elapse of time when the apparatus is left out ofoperation, the transmission factor of the optical system as a wholegradually decreases (curve A) or increases (curve B) and, at a certainlevel, it becomes substantially constant. Whether the transmissionfactor decreases or increases is determined, depending on thecharacteristic of the optical system.

The results shown in FIG. 4 may be attributable to the phenomenon thatthe moisture contained in the ambient gas within the optical system isgradually deposited on lens surfaces by which the transmission factor ischanged.

In this embodiment, dry N₂ or He gas or dry air, for example, issupplied from the purging inlet port, and the gas is then collected fromthe gas outlet port. Thus, the ambient gases inside the optical systemscan be continuously purged, by which the humidity inside the opticalsystem can be lowered and variation of transmission factor can beprevented. As a result of this, the transmission factor of the opticalsystem is substantially unchanged with the elapse of time.

FIG. 5 is a schematic view of a general structure of a projectionexposure apparatus according to another embodiment of the presentinvention. In FIG. 5, the elements corresponding to those of FIG. 1 aredenoted by like numerals. Thus, a description therefor will be omitted.

In FIG. 5, denoted by 8, 9 and 10 are hygrometers disposed inside theoptical systems, respectively, by which the level of replacement insidethe optical systems can be monitored continuously. Purging tubes areprovided with servo valves 12-17 as illustrated which can be opened andclosed as controlled by a main controller 11. These valves are normallyclosed.

If any of the monitored replacement levels (levels of hygrometers 8, 9and 10) is above a specified level as inputted into the main controller11 beforehand, the main controller 11 supplies a gas purging startsignal to a corresponding one or ones of the servo valves 12 and 13, 14and 15 or 16 and 17 to open it, whereby gas purging is initiated. If thereplacement level becomes smaller than a particular level for completiondetection as inputted into the main controller 11 beforehand, the maincontroller 11 applies a gas purging completion signal to thecorresponding servo valve to close the same. By this, gas purging isstopped. The gas purging may be completed in response to the elapse of apredetermined time from the gas purging start. Alternatively, completiondetection based on replacement level and completion detection responsiveto elapse of a predetermined time may be used in combination.

FIG. 6 is a schematic view of the structure of an exposure apparatusaccording to a third embodiment of the present invention. This exposureapparatus includes an exposure light source 101, an illumination opticalsystem 102, a projection optical system 104, a reticle (mask) R, aphotosensitive substrate (wafer) W, and a substrate stage 105 on whichthe wafer W is placed. Among these components, the exposure apparatusmajor assembly excluding the exposure light source 101 is accommodatedin a chamber 120 which is controlled at a constant temperature.

The exposure light source 101 may comprise an excimer laser of KrF(wavelength 248 nm), ArF (wavelength 193 nm) or F₂ (wavelength 157 nm),for example, for producing pulse light in the ultraviolet region. Inplace of such an excimer laser, an Hg lamp may be used as an exposurelight source, and i-line (wavelength 365 nm) may be used as exposurelight.

The illumination optical system 102 comprises a number of opticalelements such as lenses or mirrors, and it serves to illuminate anillumination region on the reticle R with uniform illuminance, with theexposure light from the exposure light source 101. This illuminationoptical system 102 is accommodated in two casings 110 and 111 which aresealingly closed. The illumination optical system 102 includes a beamshaping optical system 106, a zooming optical system (enlarging system)107, a fly's eye lens 108 as an optical integrator, and an illuminationsystem aperture stop 109 disposed at the exit of the fly's eye lens 108.The second casing 111 contains a condenser lens 112. Between the firstcasing 110 and the second casing 111, there is a blind 113 fordetermining the shape of the illumination region on the reticle R. Atthe portions of the first and second casings 110 and 111 which are onthe path of exposure light (illumination light), there are transparentglass windows.

Details of the structural portions of the illumination optical system aswell as the functions of them will be described. The exposure lightemitted from the exposure light source 101 passes through the beamshaping optical system 106 by which the beam shape is changed from anoblong shape to a square shape. Then, the light enters the zoomingoptical system (enlarging system) 107, whereby the exposure light isenlarged to a required size. The light then enters the fly's eye lens108. The exit side end face of the fly's eye lens 108 is in an opticallyconjugate relation with the light source 2, and a secondary light sourceplane is defined there. Light rays emitted from the secondary lightsources (elements) go through the aperture of the aperture stop 109 andthe blind 113, by which the illumination region on the reticle R isrestricted. The exposure light impinging on the condenser lens 112 iscollected, and then it illuminates the reticle R which is placed in apositional relation of Fourier transformation with respect to thesecondary light source plane. Thus, the individual elements of the fly'seye lens 108 illuminate the reticle R through the condenser lens 112,such that they serve as an optical integrator. As a result, the patternregion of the reticle R is illuminated uniformly.

The projection optical system 104 comprises a lens barrel and plurallens elements supported by the barrel. The projection optical system 104has a pupil plane which is in an optically conjugate positional relationwith the secondary light source plane and also in a positional relationof Fourier transformation with respect to the reticle surface.Illumination light diffracted by the pattern on the reticle R enters theprojection optical system 104, and diffraction light passing through anaperture stop (not shown), defined at the pupil plane of the projectionoptical system 104, serves to project the pattern of the reticle R ontothe wafer W which is disposed at a position optically conjugate with thereticle R.

The substrate stage 105 for holding the wafer W can be movedtwo-dimensionally by means of a driving system, not shown. Thus, byperforming exposures while stepping the substrate stage 105, the patternof the reticle R can be transferred to different shot areas on the waferW sequentially.

In the projection exposure apparatus of this embodiment as describedabove, a nitrogen supplying device 114 is connected to the casings 110and 111 of the illumination optical system and to the projection opticalsystem 104 through tubes, for supplying a dry inert gas (nitrogen N₂gas) so as to keep a low “oxygen” density inside the casings 110 and 111and the projection optical system 104. Also, a gas evacuating device 115is connected to them through tubes, for discharging the inside air orgases in them. Additionally, the nitrogen supplying device 114 and thegas discharging device 115 are connected to the inside of each barrel,constituting an optical system accommodated in the casing and having anumber of lenses therein, so that a low oxygen density is keptconstantly also inside the barrel.

FIG. 7 is an enlarged view showing an example of a casing 121 and abarrel 122 accommodated in the casing 121. As shown in FIG. 7, thebarrel has lenses 123 a-123 d disposed therewithin. There are spaces 124a-124 e as separated by these lenses 123 a-123 d. Mounted at theopposite ends of the barrel 122 are sheet glass members 125 a and 125 bas windows, and they are demountably mounted. The inside space of thecasing 121 and the inside space of the barrel 122 are communicated witha nitrogen supplying device, not shown, through tubes 126 a and 126 b,and also they are communicated with a gas discharging device, not shown,through tubes 127 a and 127 b. By continuous or interrupted nitrogen gasreplacement, the oxygen density within the casing 121 and the barrel 122can be maintained at a low level. However, the spaces separated withinthe barrel 122 are in a closed state, and it can be considered thatthere is substantially no flow of gas or air between them.

In consideration of this, in the present embodiment, for circulation ofnitrogen within these spaces, end portions of the lenses 123 a-123 doutside the effective light flux are removed to positively provide aflow passage there. FIG. 8 shows examples wherein lens portions outsidethe effective light flux are removed. In FIG. 8, denoted at 131 is alens, denoted at 132 is the effective light flux range, and denoted at133 is a notch.

As shown in FIG. 7, the lenses 123 a-123 d with notches are disposedwith a shift so that the flow patch does not extend along a straightline. This ensures that the nitrogen gas can be supplied into the wholespaces 124 a-124 e uniformly. The projection lens 104 may have a similarstructure, by which nitrogen circulation within the whole spacesseparated by the lenses can be accomplished.

In accordance with the embodiments of the present invention as describedabove, a flow path for circulation of inert gas such as nitrogen withinthe spaces separated by lenses inside a barrel can be provided with asimple design and without an increase in size of a barrel or lens.

Next, an embodiment of a device manufacturing method which is based onan exposure apparatus or exposure method such as described above, willbe explained.

FIG. 9 is a flow chart of a procedure for the manufacture ofmicrodevices such as semiconductor chips (e.g., ICs or LSIs), liquidcrystal panels, CCDs, thin film magnetic heads or micro-machines, forexample. Step 1 is a design process for designing a circuit of asemiconductor device. Step 2 is a process for making a mask on the basisof the circuit pattern design. Step 3 is a process for preparing a waferby using a material such as silicon. Step 4 is a wafer process which iscalled a pre-process wherein, by using the so prepared mask and wafer,circuits are practically formed on the wafer through lithography. Step 5subsequent to this is an assembling step which is called a post-processwherein the wafer having been processed by step 4 is formed intosemiconductor chips. This step includes an assembling (dicing andbonding) process and a packaging (chip sealing) process. Step 6 is aninspection step wherein an operation check, a durability check and so onfor the semiconductor devices provided by step 5, are carried out. Withthese processes, semiconductor devices are completed and they areshipped (step 7).

FIG. 10 is a flow chart showing details of the wafer process. Step 11 isan oxidation process for oxidizing the surface of a wafer. Step 12 is aCVD process for forming an insulating film on the wafer surface. Step 13is an electrode forming process for forming electrodes upon the wafer byvapor deposition. Step 14 is an ion implanting process for implantingions to the wafer. Step 15 is a resist process for applying a resist(photosensitive material) to the wafer. Step 16 is an exposure processfor printing, by exposure, the circuit pattern of the mask on the waferthrough the exposure apparatus described above. Step 17 is a developingprocess for developing the exposed wafer. Step 18 is an etching processfor removing portions other than the developed resist image. Step 19 isa resist separation process for separating the resist material remainingon the wafer after being subjected to the etching process. By repeatingthese processes, circuit patterns are superposedly formed on the wafer.

With these processes, high density microdevices can be manufactured.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. An exposure apparatus, comprising: anillumination optical system for illuminating an original with an F₂excimer laser; a projection optical system for projecting a pattern ofthe original onto a substrate to be exposed; gas purging means forreplacing a gas in an inside space, which accommodates opticalcomponents of at least one of said illumination optical system and saidprojection optical system, with a dry gas; a hygrometer, disposed in theinside space, for measuring conditions in the inside space and forproducing an output; and a controller for controlling said gas purgingmeans on the basis of the output of said hygrometer.
 2. An apparatusaccording to claim 1, wherein the dry gas consists of one of N₂ gas, Hegas and dry air.
 3. An apparatus according to claim 1, furthercomprising passage means, mutually communicating spaces separated bysaid optical components, for assisting in gas purging by said gaspurging means.
 4. An apparatus according to claim 1, further comprisinga path defined within the space for allowing gas to flow from a gasinlet to a gas outlet, for assisting in gas purging by said gas purgingmeans.
 5. An exposure apparatus, comprising: an illumination opticalsystem for illuminating an original with ultraviolet light; a projectionoptical system for projecting a pattern of the original onto a substrateto be exposed; gas purging means for replacing a gas in an inside space,which contains optical components of at least one of said illuminationoptical system and said projection optical system, with a particulargas; passage means, mutually communicating spaces separated by saidoptical components, for assisting in gas purging by said gas purgingmeans; and supports for supporting said optical components, wherein saidpassage means comprises apertures formed in said supports or saidoptical components, and wherein a straight line connecting apertures ofa pair of adjacent supports of said passage means is not parallel to aplane defined by an optical axis of a lens which is one of the opticalcomponents and a straight line connecting apertures of another pair ofadjacent supports.
 6. An apparatus according to claim 5, wherein theparticular gas consists of an inert gas.
 7. An apparatus according toclaim 5, further comprising a path defined within the space for allowinggas to flow from a gas inlet to a gas outlet, for assisting in gaspurging by said gas purging means.
 8. An apparatus according to claim 5,further comprising a light source that includes an F₂ excimer laser. 9.An exposure apparatus comprising: an illumination optical system forilluminating an original with ultraviolet light; a projection opticalsystem for projecting a pattern of the original onto a substrate to beexposed; gas purging means for replacing a gas in an inside space, whichcontains optical components of at least one of said illumination opticalsystem and said projection optical system, with a particular gas, saidoptical components comprising at least one lens; and passage means,mutually communicating spaces separated by said optical components, forassisting in gas purging by said gas purging means, wherein said passagemeans comprises a notch provided on said at least one lens.
 10. Anapparatus according to claim 9, wherein the particular gas consists ofan inert gas.
 11. An exposure apparatus, comprising: an illuminationoptical system for illuminating an original; a projection optical systemfor projecting a pattern of the original onto a substrate to be exposed;gas purging means for replacing, with a particular gas, a gas in aninside space which contains optical components of at least one of saidillumination optical system and said projection optical system, saidoptical components comprising at least one lens; and a plurality ofpassage means, mutually communicating spaces separated by said opticalcomponents, for assisting in gas purging by said gas purging means,wherein a straight line connecting an adjacent pair of said plurality ofpassage means provided in a same casing for gas purging, is not parallelto an optical axis of said at least one lens and a straight lineconnecting another pair of said plurality of passage means, which is oneof the optical components.
 12. An apparatus according to claim 11,wherein the particular gas consists of an inert gas.
 13. A devicemanufacturing method, comprising: illuminating an original with an F₂excimer laser using an illumination optical system; projecting, using aprojection optical system, a pattern of the original onto a substrate tobe exposed to manufacture a device; replacing, using gas purging means,an inside space, which accommodates optical components of at least oneof the illumination optical system and the projection optical system,with a dry gas; measuring, using a hygrometer disposed in the insidespace, conditions in the inside space and producing an output; andcontrolling the dry gas replacement using the gas purging means, on thebasis of the output of the hygrometer.
 14. A method according to claim13, wherein the dry gas consists of one of N₂ gas, He gas and dry air.15. A device manufacturing method, comprising: illuminating an originalwith ultraviolet light using an illumination optical system; projecting,using a projection optical system, a pattern of the original onto asubstrate to be exposed to manufacture a device; replacing, using gaspurging means, an inside space, which contains optical components of atleast one of the illumination optical system and the projection opticalsystem, with a particular gas, the optical components comprising atleast one lens; mutually communicating, using passage means, spacesseparated by the optical components, for assisting in gas purging by thegas purging means; and supporting the at least one lens using a support,wherein the passage means comprises an aperture formed in the supportand, wherein a straight line connecting apertures of a pair of adjacentsupports of said passage means is not parallel to a plane defined by anoptical axis of a lens which is one of the optical components and astraight line connecting apertures of another pair of adjacent supports.16. A method according to claim 15, wherein the particular gas consistsof an inert gas.
 17. A device manufacturing method, comprising:illuminating an original with ultraviolet light using an illuminationoptical system; projecting, using an illumination optical system, apattern of the original onto a substrate to be exposed to manufacture adevice; replacing, using gas purging means, an inside space, whichcontains optical components of at least one of the illumination opticalsystem and the projection optical system, with a particular gas, theoptical components comprising at least one lens; and mutuallycommunicating, using passage means, spaces separated by the opticalcomponents, for assisting in gas purging by the gas purging means, thepassage means including a notch provided on the at least one lens.
 18. Amethod according to claim 17, wherein the particular gas consists of aninert gas.
 19. A device manufacturing method, comprising: illuminatingan original using an illumination optical system; projecting, using aprojection optical system, a pattern of the original onto a substrate tobe exposed to manufacture a device; replacing with a particular gas,using gas purging means, an inside space which contains opticalcomponents of at least one of the illumination optical system and theprojection optical system, the optical components comprising at leastone lens; and mutually communicating, using a plurality of passagemeans, spaces separated by the optical components, for assisting in gaspurging by the gas purging means, wherein a straight line connecting anadjacent pair of said plurality of passage means provided in a samecasing for gas purging, is not parallel to a plane defined by an opticalaxis of said at least one lens and a straight line connecting anotheradjacent pair of said plurality of passage means.
 20. A method accordingto claim 19, wherein the particular gas consists of an inert gas.